Mobile networks are currently evolving from pure circuit switched (CS) networks towards packet switched (PS) networks, in particular Internet Protocol (IP) based networks, and by that integrate into IP based infrastructures that are also used for the Internet, the World Wide Web, and the datacom industry.
More specifically, technologies allowing voice communication over an IP based network have been introduced. Examples of such technologies are Voice over IP (VoIP) via Digital Subscriber Line (DSL) access or Voice over IP via Wireless Local Area Network (WLAN) access. Also in some mobile networks, technologies which allow voice communication over an IP based network are available. Examples of such mobile networks are mobile networks as specified by the 3rd Generation Partnership Project (3GPP). For example, a mobile network may implement an IP Multimedia Subsystem (IMS) as specified in 3GPP Technical Specification (TS) 23.228 V12.0.0 and offer voice communication as an IMS service.
Further, a concept referred to as IMS Centralized Services (ICS) has been introduced which allow for utilizing IMS services over various types of access networks, including not only PS access networks, but also CS access networks. The ICS concept is for example specified in 3GPP TS 23.292 V12.1.0. Using the ICS concept, the IMS voice services may be available via various kinds of radio access technology (RAT), such as Global Systems for Mobile Communications (GSM), Wideband Code Division Multiplex (WCDMA), General Packet Radio Service (GPRS), Enhanced Data Rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), Universal Mobile Telecommunications System (UMTS), and High Speed Packet Access (HSPA). Voice communication with a user equipment (UE) which is connected to the mobile network via a CS access network may then be routed through the IMS.
For scenarios where IMS services are usable by a UE both via PS access networks and via CS access networks, a mechanism referred to as Terminating Access Domain Selection (T-ADS) was introduced to select between multiple possible access types for terminating a call to a UE. The T-ADS mechanism is for example specified in 3GPP TS 23.401 V12.0.0, 23.060 V12.0.0, and 23.292 V12.0.0. According to these specifications, T-ADS may be implemented by a Service Centralization and Continuity Application Server (SCC AS) as for example specified in 3GPP TS 23.237 V12.2.0. The T-ADS functionality of the SCC AS may apply various criteria for selecting between a CS access network or PS access network for terminating an incoming voice session. For example, the SCC AS may obtain capabilities of the most recently used PS access network, e.g., in the form of an “IMS voice over PS session supported indication” and current RAT type, from a subscriber database referred to as Home Subscriber Server (HSS).
In addition, It is known to integrate Wireless Local Area Network (WLAN) accesses (also referred to as WiFi accesses) into the mobile network infrastructure. Specifically, control functionalities for such WLAN accesses may be integrated in the core network of the mobile network. Such concepts are for example described in 3GPP TS 23.402 V12.0.0 and 3GPP Technical Report (TR) 23.852 V1.5.0.
If a UE is attached to the mobile network via such WLAN access and loses WLAN coverage, a handover to a cellular network access may be triggered by the UE. For example, the triggering of such handover may be governed by ANDSF (Access Network and Domain Selection Function) policies. The ANDSF is for example described in 3GPP TS 23.402. Such handover procedures are for example described in 3GPP TS 23.060, 23.401, and 23.402. The details of such procedure depend on the particular scenario.
For example, if the UE is not connected to a cellular network access when it loses WLAN coverage, and the UE wants to preserve its IP address when moving to the cellular network access, it may perform a so called “handover attach” in to the cellular network access. The handover attach is similar to a usual attach to the cellular network access, but indicates “handover” as the request type. The handover indication is forward to the Packet Data Network Gateway (PGW) used for the cellular network access. The PGW may then continue to use the IP address which was used over the WLAN access also for the cellular network access.
If the UE already has packet data network (PDN) connectivity via a cellular network access, it may in turn initiate establishment of a new PDN Connection via the cellular network access, which then uses the IP address which was also used for the WLAN access. Also in this case, the above-mentioned “handover” indication may be used to indicate that the IP address of the UE should be preserved.
The above mechanisms of preserving the IP address allow for using a single registration of the UE in the IMS, irrespective of the UE being on a WLAN access or on a cellular network access. However, certain IMS services may then not be aware whether the UE is on a WLAN access or on a cellular network access. For example, if an IMS voice call to the UE needs to be terminated, the T-ADS functionality of the SCC AS may not be able to determine whether the UE is on a WLAN access or on a cellular network access. Accordingly, such information cannot be used by the T-ADS functionality. Problems may then for example arise if termination of the IMS voice call over WLAN is not possible due to restrictions of the WLAN access or if such termination is not desirable for other reasons. Similar problems may also exist for other services provided to the UE.
Accordingly, there is a need for techniques which allow for efficiently controlling communication of a UE in a mobile network.